Tuned transformer assembly



Feb 0, 1948. 1.. G. KETCHAM 2,435,630

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TUNED TRANSFORMER ASSEMBLY Filed June 2, 1945 5 Sheets-Sheet 3 INVENTOR. J8 LY/VA/V 6 Kira/144m arroewz Y5 meme Feb. 10, 1948 2,435,630 TUNED TRANSFORMER ASSEMBLY Lyman G. Ketcham, Kearny, N. 1., asslgnor to Automatic Manufacturing Corporation. East Newark, N. 1., a corporation of New Jersey c Application June 2, 1945, Serial No. 587,349 12 Claims. (Cl. 171-111) This invention pertains to tuned, high frequency transformer assemblies and, more particularly, to such as are adapted for use in the intermediate frequency portion of superheterodyne radio receiving systems and the like, and such as are commonly referred to as intermediate frequency, or more simply as I. R, transformers.

Intermediate frequency or I. F. transformers, in general, consist of a pair of magnetically coupled coilsconstituting primary and secondary transformer windings, with tuning capacities connected in shunt, to'said coils respectively. The capacities tune the coils to the desired frequency range of transmission, and the coils are slightly over-optimum coupled, to provide-band transmission throughout the desired transmission range with relatively sharp cut-oil at the limiting transmission frequencies.

From the standpoint of tuning, I. F. transformers may be generally classified in either of two categories, i. e., those which employ capacity tuning and those which employ inductance tuning.

The conventional capacity tuned I. F. transformer consists of mica dielectric, compression type capacitors which are usually assembled on a ceramic base. The coil form on'which the magnetically coupled coils or inductances are wound.

is secured to thecapacitors, and the entire unit is assembled in a metal shielding can. The external terminals are ordinarily in the form of flexible, insulated leads which can be soldered directly to the'tube sockets. The major disad vantages of the capacity tuned transformers are: instability due to temperature and humidity changes; difficultles of precise tuning due to relatively large changes of capacity with small variations of the adjusting screw; and variations of capacity coupling due to changes in spacing of coil leads and external leads. Various means have been proposed for overcoming one or all of these objections, but, without entering into a detailed discussion thereof, suffice it to say that allentail more elaborate and expensive constructions.

.In contrast to the above, the conventional inductance tuned I. F. transformer consists of silvered mica capacitors mounted on a terminal board to which the coil form is secured. Thisis usually accomplished bymeans of threaded bush.- ings which also engage threaded metal studs molded in the powdered iron cores employed for inductance adjustments of the coils. The entire unit so constructed is assembled in a metal shield can. The external terminals are ordinarily in the form of lugs which extend through the radio chassis for wiring to the tube sockets.

The major disadvantage of the inductance or permeability-tuned transformers as heretofore constructed, is the variation of Q, i. e., the factor R of' the inductance: with changes in iron-core positions. Variation of capacity-coupling is also present in this type of transformer, but not to the same extent as in thecapacity tuned type.

Both of the capacity'tuned and inductancetuned types-of transformers aforesaid are subject to considerable-variation in mutual inductances due to mechanicalvarlations ofthe parts, and are subject-also into-various other disadvantages which need not berecounted, because well understood to those skilled in the art.

The improved transformer of the present invention is of the permeability or inductancetuned type.-- It is of extremely compact design such that. it can be assembled in a three-fourths inch: square shielding can; or in even smaller dimensions if. desired. j

The condenser assembly consists. in the preferred modification, of a single sheet of mica dielectric having on, each side thereof, in opposed relation, two silvered-areas forming the two capacitors. Whenhigher capacity values are required, two or more of suchsilvered mica sheets may be stacked and resiliently clamped. Contact is made tothe four silvered sections-by four terminal lugs, which are compressed between an insulating base :plate: and an insulating clamp plate, by means of a single central eyelet. A spring plate is interposed between the eyelet and the clamp plate for providing a'reslliently compressed, unitary assembly, in which the compressionis maintained overa wide range of temperatures and repeated-temperature cycles.

The coil assembly consists of a tubular coil form of suitable insulating material, such as laminated plastic, upon. the opposite ends; of which are wound the primary and secondary transformer coils or inductances, Two-externally threaded,

' cup-like,powdered-iron,- shell cores having internally projecting central studs integral therewith, are assembled on opposite ends of the coil form, in such fasion that the central stud of each shell core fits into the tub lar end of the coil form, and thus forms a magnetic-core forthe coil; while the outer cylindrical wall of the core fits over the coil in spaced relation thereto to-form a shield. These two shell cores and the coil form are clamped between cooperating male and female frame memb rs, of suitable insulating material, such as laminated plastic, which cooperate thereby to provide a split-nut arrangement, having suitably threaded interior surface portions for threadedly engaging the shell cores, and which are also suitably provided with semi-circularly recessed portions fitting about the central portion of the coil form for supporting the same. The components as thus arranged are maintained in unitary assembly by means of a substantially U-shaped wire spring clip, which snaps into suitable recesses provided on opposite external surfaces of the male and female frame members respectively. Slippage of the coil form is prevented by cementing it within the socket provided by the semicircular recesses in the frame members; or alternatively by providing a flange on the coil form or a pin through it and corresponding recesses in the sockets of the frame members for reception of the flange or pin.

The frame members are provided with grooves and tabs in a manner such that the four leadout wires from the coils may be definitely positioned and insulated from each other and from other parts. Also one end of each frame member is provided with tabs and shoulders to properly position the assembly in rectangular slots provided in the top of a shielding can housing the assembly. The other end of each frame member is provided with tabs and shoulders adapted to fit into appropriate recesses provided in the capacitor base for this purpose. The entire transformer and capacitor base assembly is held within the shielding can by means of tabs provided at the base of the can, which, after assembly, are bent in under the capacitor base.

The shielding can is removably mounted on the chassis of the radio receiver or the like by means of a spring mounting clip which extends through suitable slots in the chassis and snaps into truncated cut-outs provided in opposite side walls of the shielding can.

Inductance adjustment of the upper coil is made by inserting a tool through an aperture provided in the top of the shielding can, and into a recess provided in the upper surface of the shell core, and thereby rotating the shell core to vertically adjust the same, upwardly or downwardly as desired, owing to the threaded mounting of the shell core between the frame members. In this way, the shell core is caused to variably penetrate and overlap the associated coil. Similar adjustment of the lower shell core is made through the aforesaid hollow eyelet in the capacitor assembly. In this way, the effective coil inductances, and the magnetic coupling between coils, may be varied as desired within the design limits of the equipment.

Having thus described generally the construction and arrangement of the transformer assembly in accordance with the inventions and the features thereof believed novel, reference is now made to the accompanying drawings for a more detailed description thereof wherein:

Fig. 1 is a plan view of a preferred form of tuned transformer assembly in accordance with the invention; while Figs. 2 and 3 are longitudinal sections thereof taken at 2-2 and l3 of Fig. 1 respectively.

Figs. 4 to '7 are views of the cooperating male and female frame members employed for supporting the coil form and for adjustably mounting the shell cores within the shielding can; Fig. 4 being a front elevation of the female frame member, and Fig. 5 a longitudinal section thereof at 5-5 of Fig. 4; while Fig. 6 is a from; ekvation of the corresponding male frame member, and Fig. 7 is a longitudinal section thereof taken at 1-1 of Fig. 6.

Fix. a is a transverse section of the transformer assembly taken at H of Fig. 3.

Fig. 9 is a perspective view of the condenser and terminal lug assembly.

Fig. 10 is a side elevation of the shielding can employed for housing the assembly: while Fig. 11 is a perspective view of the resilient mounting clip employed for detachably securing the canencased transformer assembly to the chassis of a radio receiver or the like.

Fig. 12 is a plan view of a fragmentary showing of the chassis portion upon which the transformer assembly is mounted, this view showing the chassis apertures required for reception of the aforesaid mounting clip and for projection of the condenser terminal lugs therethrough.

Fig. 13 is a fragmentary detail of the transformer assembly showing the manner in which lead-out connections extend from the transformer coils to the terminal lugs.

Fig. 14 shows the basic circuit arrangement of the intermediate frequency transformer assembly of the invention.

Fig. 15 is a sectional view, similar to Fig. 3, but showing two tuned I. F. transformer assemblies mounted in a single shielding, for adapting a radio receiver for reception over two different frequency bands such as the broadcast band and the ultra-high frequency so-called frequency modulation band.

Fig. 16 shows the basic circuit arrangement of the Fig. 15 assembly.

Referring, for the moment, to Fig. 14 in the drawings, the intermediate frequency or I. F. transformer of the invention, consists essentially of a pair of magnetically coupled, high frequency, iron-core coils W1, W:, the inductances of which are adjustable as indicated, and across which are respectively bridged, tuning condensers C1 and C2, each coil and its associated shunt condenser being connected between a pair of input or output terminals T1 or T2.

Referring now to the remaining figures of the drawings, which show the constructional details of the assembly, and more particularly to Figs. 1 to 3 thereof, the transformer comprises a tubular insulating coil form i, of laminated plastic or the like, mounting at its opposite ends a pair of multi-layer coils 2, 3. Each coil 2, 8 is housed within a. cup-like shell core 4, 5, provided with a central stud, such as I, fitting slidably within an end of the tubular coil form I, as shown. The outer cylindrical surfaces of the shell cores 4, l. are threaded as shown and threadedly engage threaded portions of the male and female frame members 1 and 8 of Figs. 4 to '1 inc., in assembled relation in the manner shown in Fig. 3 at ii. In addition, these frame members, which are described more in detail hereinafter, are provided. as shown in Figs. 3 and 8, with inwardly extending flanges 9 and i0, having semi-circular inner surfaces, which cooperate to surround and frictionally engage the coil form I, thereby to support the same, as shown in Figs. 3 and 8. The shell cores 2, 3 are made of powdered iron admixed with a suitably powdered filler, such as a thermosetting resin and molded onto the configuration shown under heat and pressure.

Referring to Figs.- and 7 inc., the male and female frame members 1, I are of generally rectangular contour, viewed in elevation, as shown in Figs. 4 and 6, and are provided with plane exa terior surfaces H, l2 and interior surfaces II, II of arcuate contour containing, adjacent their upper and lower ends respectively, threaded portions, such as l5, for threadedly engaging the outer threaded surfaces of the shell cores 4, 5, as above noted in connection with Fig. 3. About midway of their elevations, these frame members are provided with the above-mentioned inwardly extending flanges 9, Ill, having semi-circular inner surfaces I6 supporting the coil form I, in the manner shown in provide an interlock for the frame members, at the point of support of the coil form I, the flange in of the male frame member terminates atits inner end in projecting lugs l8, which engage cor.- responding slots l9 nation of flange 9 as shown more particularly in Figs, 4 to '7 and 8.

Referring more particularly to Figs. 2, 3 and 8, the transformer i, 2, 3, shell cores 8, 5 and frame members i, 8 are held in integral assembly by means of a wire spring clip 2|], of U-shaped configuration, bent at its opposite ends into inwardly p e ng l s, such as 22, engaging slotted-re,

cesses, such as 23, provided in the frame members i, 8.

Fig, 8. In order to provided at the inner termiof the female frame member,

The transformer and frame member assembly as thus far described, i slidably housed within an open-ended metal shielding can 24, of generally rectangular, box-like contour, and provided at its upper end with oppositely disposed rectangular slots 25, Fig. l, for reception of pro iecting lugs 26, provided at the upper ends of the frame members, thereby to position the transiormer assembly within the shielding can as shown in Figs. 2 and 3.

The condensers C1, 02, for tuning the transformer coils W1, We of Fig. 14, or 2, 3 of Figs, 2 and 3, to the desired intermediate frequency range, in perspective in Fig. 9 and indicated generally by the numeral 2?. This consists of a rectangular sheet of dielectric material 211;, such as mica, the upper and lower surfaces of which are provided in shined relation, with spaced, silvered areas, such as 28, 29. Terminal lugs, such as til, are mounted against the upper silvered areas respectively, and corresponding terminal lugs are mounted against the corresponding lower silvered areas respectively.

The condenser assembly 211, as thus shown in the manner of Fig. 9, is mounted on an insulating base member 32, Figs. 2, 3, of, for example, laminated plastic material or the like. The base member is of generall rectangular contour, corresponding to that of the condenser assemply 2i, and is provided with downwardly projecting studs, such as 33, Figs. 2, 3 and 12, which are slotted as shown at 35, Fig, 12, and through the slots of which, extend the terminal lug 30, iii of the condenser assembly.

Viewed in end elevation, the upper portion of the base member 32 is of channel-like configuration, and provided with opposite upwardlyem tending side-wall portions, such as 35, Fig. 2, adapted to receive and center a rectangular clamp plate 36 of insulating material, such as laminated plastic or the like. The clamp plate 36 is slightly channeled on its upper surface, as shOWn at 3'5, Figs, 2 and 3, for reception of a spring plate 38 of slightly U-shaped configuration. The spring plate 38, clamp plate 36. condenser structure 21, terminal lugs 30, 3|, and base member 32, are all centrally apertured, as shown, for reception of a metal eyelet 39, Figs. 2 and 3, which extends are constructed in the unitary form shown clip 5i, Fig. 11.

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through the apertures of the assembly and is bent, at its upper end, over the spring plate, as at 40. and,'at its lower end, over the base plate, as at H, for providing a unitary assembly of these elements, maintained under resilient compression by the action of the spring plate 38.

This unitary assembly, held together by eyelet 39,- is slidably housed within the lower portion of the shielding can 24 below the fram members I, 8, as shown in Figs. 2 and 3. For maintaining the frame '1, lassembly'and. the base 32, 21, 36 assembly in proper relation to each other, the upstanding side walls 5-35 of the base are longitudinally slotted for reception, as shown at 42, 3 of Fig, 3, of thedownwardly extending tabs 42, 43, Figs, 4 to 7 inc, provided at the lower ends of the frame members 1, Q. It will be observed, in this connection, that tab 42 on the female frame member l is somewhat shorter than the corresponding stud 43 on the male frame member 8. The reason for this is shown in Fig. 3, wherein the slot provided in the side wall 35 on base 32 for reception of the female frame member stud 42, terminates abruptly as shown at M, to provide a support for frame member 1; while the corresponding slot provided in the opposite side wall base, for reception of the male frame member stud 43, i cut through as shown at 45, Fig. 3, so that the entire support for the coil and frame member assembly, as integrated by the wire spring clamp 20, is provided on the shoulder M of the base member 32. I

The shielding can fit is'provided initiall with downwardly projecting tabs Fig. 10, integral. with the side walls thereof. These tabs are for the purpose of holding the frame and base assemblies in their assembled relation as shown in Figs. 2- and 3, to which end, after being so assembled, these tabs 56 are bent inwardly under the base plate 52, as shown in Fig. 2.

The entire assemblage, as thus housed within the shielding can, is mounted on the chassis il, Figs. 2, 3 and 10, of a radio receiver or the like, the chassis being appropriately apertured, as at (Fig 12, for projection therethrough of the base member studs 33, and the terminal lugs til, 38 extending therein.

For securing the shielding can 24 to the chassis member ll, the shielding can is provided on its opposite side walls as 39, Fig. id, for shaped lugs Ell with truncated apertures, such reception of correspondingly provided on a U-shaped spring The chassis member 41 is provided with appropriately spaced rectangular slots t2, Fig. l2, through which the lugs 50 of the spring clip iii are pushed from the lower side of the chassis and the lugs 50 thereupon snapped into position in the can apertures #39, as shown in Fig. 2.

Referring to Figs. 4 to 8 and 13, the central.

flanges 8, it of the frame members i, t are rv vided with laterally extending flanged and grooved portions. 53, 54, 55; while the lower vertical portions of the frame members proper are provided with laterally projecting tabs, such as 56, ill, 58 for bringing out the lead-out wires, such as 59, 50, from the coils 2, 3, in the manner illustrated in Fig. 13. Thus, referring more particularly to Fig. 13, lead-out conductor 59 extending from the upper coil 2 is extended downwardly from the coil and looped under flange 53 on frame member '8, and is passed thence along the groove 54 and over the outer shoulder of flange 55, and laced thence under the first tab 56, over the second .tab 5'! and under the bottom tab 58,

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these tabs BI, 51, ll having surfaces contacting the lead-out conductors which are alternately beveled in opposite directions for maintaining the conductor in position as shown. The second lead-out from coil 2, not shown, is brought out on the opposite side of the coil, and similarly extended over the opposite flanges and grooves 53 to 58. Fig. 4. In the same manner, the lead-outs, such as 60, extending from the lower coil 3, are passed up and over the inner shoulder of flange 85, thence down over the outer shoulder thereof and laced through the tabs 80, 51, It in accordance with the showing of Fig. 13.

As above stated, the powdered iron shell cores 4, 5 are mounted in threaded engagement with the frame members 1, 8 as shown more particularly in Figs. 2 and 3. For vertically adjusting the upper shell core 4 in relation to its associated v coil 2, an aperture ii is provided in the upper end of the shielding can 24, and also a recess, for example, rectangular, hexagonal, etc., is provided in the upper surface of shell core 4. Adjustment is effected by inserting a suitable tool through the can aperture 8i into the shell core recess 62 and rotating the tool. Similarly, for vertically adlusting the lower shell core 5. a corresponding recess 63 is provided in the lower surface thereof, and the central eyelet 39 of the capacitor base provides an aperture for insertion of the adjusting tool through the eyelet and into the recess 61. In this way, the effective inductances of coils 2, 3, and the mutual inductance between these coils, may be adjusted as desired, within limits.

Figs. 15 and 16 show an I. F. transformer assembly and circuit arrangement for use in a receiver designed for reception over two distinct frequency bands, such, for example, as the usual broadcast band of about 535 to 1620 kilocycles employing amplitude modulation of signals; and the ultra-high frequency band of about 78 to 108 megacycles, employing frequency modulation. For this purpose, two tuned 1.1". transformer assemblies are required, one designed for a relatively low intermediate frequency of about 455 kilocycles for reception over the broadcast band, and the other designed for a relatively high intermediate frequency range of about 12 to 16 megacycles for reception over the frequency modulation or FM band.

The low frequency transformer assembly is shown at the right in Fig. 15, and is designated generally by the numeral '4. The coils 08 and 66 are of the multi-layer type mounted on an insulating coil form 6'! in the same manner as Fig. 3, this assembly being otherwise identical in all respects with that of Fig. 3 and hence requiring no further description.

The high frequency transformer assembly is shown at the left in Fig. 15, and is designated generally by the numeral II. The transformer coils in this assembly are of the single layer type, each consisting of a relatively few spaced turns, as shown at 69, 10. In this case, of course, some redesign of the iron cores 'Ii, 12 is required to provide proper spacing, as at 13, I4, between the central stud and the outer shell of the core, to adjust the air gap in conformity with the smaller coils employed; but in other respects the construction of the high frequency assembly "3 is generally the same as the low frequency assembly 64.

The two transformers are assembled side-byside, as shown in Fig. 15, in a single shielding can 15, which is generally similar in construction to that shown and described in connection with Figs.

1 to 12 inc., with the exception that it is approximately twice as wide, is provided with two sets of cut-outs, such as 13, and associated attaching clips, such as I1, one for each transformer. Also, the upper surface of the can is provided, along its opposite edges, with a pair of enlarged central cut-outs, as at 18, for reception of the adjacent centering lugs, such as ll, ll, of the adjacent frame members ll, 82 of the high and low frequency transformers respectively.

Fig. 16 shows the basic circuit arrangement for the Fig. 15 assembly. The low frequency tuned transformer 84 comprises the magnetically coupled coils 65, 6O bridged respectively by condensers 83, 84. Similarly, the high frequency tuned transformer 68 comprises the inductively coupled coils 89, HI, bridged respectively by condensers 85, 85. The low and high frequency coils 6B, 69 and 68, Hi, with their associated condensers, are connected in series, respectively, between input and output terminals 81, II, as shown. With this arrangement, and during reception of signals in the high frequency band, condensers 83, 84 act as by-pass condensers of negligible impedance across the low frequency coils 65, 88, so that the entire circuit operates as a high frequency tuned I. F, transformer. On the other hand, during reception of signals in the low frequency band, the high frequency coils 63, Hi offer negligible impedance so that the entire circuit functions as a low frequency tuned I. F. transformer.

In accordance with a further feature of the invention, the transformers may be so constructed as to compensate for variations in inductance, such as would otherwise result from temperature variations. For example, referring to Fig. 3, as the temperature increases, the radius of the transformer coils 2, 3 will increase slightly, thereby increasing the coil inductances. To compensate for this effect, the coil form i on the one hand, and the frame members I, 8 on the other, may be made of materials having different coefficients of expansion and such that, for example, as the temperature increases, thereby to increase the eflective inductance of coils 2, I, the frame members will expand at such relative rates in relation to the expansion of coil form i as to back the shell cores 4, I slightly away from their associated coils 2, 3, thereby to reduce the effective coil inductances in substantially the same proportions as they tend to be increased by expansion of the coil diameters. For example, polystyrene synthetic resin has a higher coemcient of expansion than a phenol-formaldehyde resin. Accordingy, if coil form I is made of laminated plastic material employing a phenol-formaldehyde resin, while the frame members are made of polystyrene, and the dimensions from the point of support 9, i ll of the coil form I are properly proportioned, compensation of the above character may be obtained within a desired degree of precision. The above modification will give negative temperature compensation. By reversing the materials, 1. e. by making the frame members I, l of phenol-formaldehyde resin, and the coil form of polystyrene, a positive temperature compensation may be obtained, should such become desirable for a particular construction.

What is claimed is:

1. A coil assembly of the character described, including a coil form, a coil enclosing said coil form, a magnetic core having a portion enclosed by said coil form and coil and mounted to afford 1i adjustment of the extent of its penetration within the coil, said yond one end of said coil, and a supporting frame having portions engaging the projecting portion of said coil form to hold said coil and coil form in position, ing said coil and having portions engaging said core to position the latter with respect to said coil form and coil.

2. A coil assembly of the character described, including a coil form. form, a magnetic core having a portion enclosed by said coil form and coil and mounted to afiord adjustment of the extent of its penetration within the coil, said coil form projecting axially beyond one end of said coil, and a supporting frame having portions engaging the projecting portion of said coil form to hold said coil and coil form in position, said core having a shell portion surrounding said coil, and said frame having portions disposed outwardly of and engaging said shell portion to position said core with respect to said coil form and coil.

3. A coil assembly of the character described, including a coil form, a coil enclosing said coil term, a magnetic core having a portion enclosed by said coil form and coil and mounted to afiord adjustment of the extent of its penetration within the coil, said coil form projecting axially beyond one end of said coil, a sectional frame supporting said coil form, coil and core assembly, said frame having a plurality of sections each partially enclosing said coil and core and each of said sections having portions engaging the projecting portion of said coil form to hold said coil and coil form in position, said sections also having portions engaging said core to position the latter with respect to said coil form and coil.

4. A coil assembly of the character described including a coil form, coils enclosing said coil form in spaced relation to each other, magnetic cores each having a portion enclosed by said coil form and one of said coils, at least one of said cores being mounted to afford adjustment of the extent of its penetration within its corresponding cell, and a supporting frame having sections each extending partially around the peripheries oi? the coils, said sections having inwardly projecting portions gripping between them the portion of said coil rorm between said cells to hold said coils and coil rorm in position.

5. A coil assembly of the character described including a coil form, coils enclosing said coil form in spaced relation to each other, magnetic cores each having a portion enclosed by said coil form and one of said coils, each of said cores being mounted to afford adjustment of the extent or its penetration within its corresponding coil, each of said cores having a shell portion surrounding its'correspondlng coil. and a supp rting frame having portions engaging the portion of said coil form between said coils to hold said coils and coil form in position, said frame also having portions engaging the shell portions of said cores to position the latter with respect to said coil forms and coils.

6. A coil assembly of the character described including a coil form, coils enclosing said coil form in spaced relation to each other, magnetic cores each having a portion enclosed by said coil form and one of said coils, each of said cores being mounted to afford adjustment of the extent of its penetration within its corresponding cell, each of said cores having a shell portion surrounding .its corresponding coil, said shell portions of the cores being externally threaded, and

said frame at least partially enclosa coil enclosing said coil coil form projecting axially be- 7 a sectional frame supporting said coil form, coil and core assembly, said frame having a plurality of sections each partially enclosing said coil and core, said sections having portions engaging the portion of the coil form which is between said coils to hold the said coils and coil form in position, said sections also engaging the aforesaid threaded portions of said cores,

'7. A coil assembly of the character described, including a coil form, a coil enclosing said coil form, a magnetic core having a portion enclosed by said coil form and coil and mounted to aflord adjustment of the extent of its penetration within the coil, said coil form projecting axially beyond one end of said coil, a sectional frame supporting said coil form, coil and core assembly, said frame having a plurality of sections each partially enclosing said coil and core, and means projecting inwardly from said sections and engaging the projecting portion of said coil form to hold said coil and coil form in position, and a spring clip embracing said frame sections to clamp them in position.

8. A coil assembly or the character described, including a coil form, a coil enclosing said coil form, a magnetic core having a portion enclosed by said coil form and coil and mounted to afiord adjustment of the extent of its penetration within the coil, a frame supporting said coil and coil form in position, said frame having sections each extending partially around the periphery of said coil and core, said core also having portions extending outwardly into contact with said frame sections, said frame sections also engaging one of said coil and coil form elements, and means for urging said frame sections toward each other to hold said coil form, coil and core in position.

9. A coil assembly of the character described, including a coil form, a coil enclosing said coil form, a magnetic core having a portion enclosed by said coil form and coil and mounted to afiord adjustment of the extent of its penetration within the coil, a frame supporting said coil and coil form in position, said frame having sections each partially enclosing said coil and core, and means for holding said frame sections in position, said frame sections having portions projecting endwise of said coil and engaging said core to hold the latter in position.

1o. A coil assembly of the character described, including a coil form, a coil enclosing said coil form, a magnetic core having a portion enclosed by said coil form and coil and mounted to afford adjustment of the extent of its penetration within the coil, a frame supporting said coil and coil form in position, said frame having sections each partially enclosing said coil and core, and means for holding said frame sections in position, said grame sections having portions projecting endwise of said coil and engaging said core to hold the latter in position, said last mentioned portions of the frame being spaced outwards of said coil, and said core having a shell portion interposed between said last mentioned frame portions and the coil.

11. A coil assembly of the character described, including a coil form, a coil enclosing said coil form, a magnetic core having a portion enclosed by said coil form and coil and mounted to afford adjustment of the extent of its penetration within the coil, said coil form projecting axially beyond one end of said coil, and a supporting frame having sections each extending partially around the periphery of the coil, said sections having inhaving threaded portions wardl projecting portions srilming between them the projecting portion or said coil form to hold said coil and coil form in position, said frame also having portions spaced radially outwards 01' said coil. and said core having a shell portion interposed between said last mentioned frame portions and the coil.

12. A coil assembly of the character described, including a coil form; a coil enclosing said coil form, a magnetic core having a portion enclosed by said coil form and coil and also having a shell portion constructed to surround the coil, said core being movable axially with respect to said coil, a supporting frame at least partially enclosing said coil, the surface oi said shell portion of the core adiustably engaging said supporting frame to position the core axially with respect to the coil.

LYMAN G. KETCHAM. Res-mucus mm The following references are oi record in the file oi this patent:

Number Number 12 UNITED STATES PA'I'EN'IB Name Date Marvel Jan. 17, 1929 London Apr. 14, 1931 Ketchazn Dec. 29, 1938 Jacob Mar. 15, 1938 Polydoroi! Apr. 12, 1933 Harvey Nov. 21, 1939 Loughlin May 7, 1940 rm July 2, 1940 Kirk Nov. 12, 1940 Hartl Nov, 26, 1940 Harvey May 28, 1942 Nowak Oct. 28, 1943 Gray June 15, 1940 Btahl Nov. 7, 1944 Harvey Dec. 6, 1944 Ricker July 3, 1945 Howe Nov. 13, 1943 FOREIGN PATENTS 7 Country Date Great Britain Oct. 10, 1940 

